1. Field of the Invention
The present invention relates to a control and method for extracting water from a clothes load within an automatic washer.
2. Description of the Prior Art
At the end of a wash cycle in an automatic washer there is a water extraction step in which normally the wash basket is rotated about its axis to cause water carried within the clothes load to be extracted by centrifugal force.
The speed at which the clothes basket is spun is a balancing of several factors. First, as high a speed as is feasible is desired in order to provide maximum extraction of the water from the clothes so that less energy is required in a subsequent drying step in the wash process. A number of factors enter into placing a ceiling or upper limit on the spin speed including the important consideration of attempting to avoid excessive wrinkling of the clothes, particularly permanent press type clothing. Wrinkling of the clothes is increased when the clothes are spun at a very high rotational rate. Automatic washing machines manufactured by Whirlpool Corporation, the assignee of the present application, have a top spin speed in the range of 600-700 rpm, in that it has been determined that higher spin speed causes excessive wrinkling.
A common prior art method of spinning the basket incorporates an AC motor which, through an appropriate transmission and gearing quickly accelerates the basket up to a constant speed level which is maintained throughout the entirety of the extraction step for a predetermined length of time.
Other types of extraction controls and methods are known in the art. U.S. Pat. No. 2,975,902 discloses a horizontal axis washer in which the spin speed is increased in small predetermined increments from a normal tumbling speed up to the speed at which the clothes become plastered against the drum wall in order to effect a desired distribution of the clothes around the drum wall. Once the clothes have become plastered against the wall, the spin speed is then increased rapidly to a maximum spin speed.
U.S. Pat. No. 3,403,538 discloses the use of a controlled spin operation in which the spin speed is prevented from rising above 300 rpm during a first phase of spin, but is permitted to increase to a speed between 300 rpm and 1000 rpm during a second phase of spin if an unbalanced load was not detected as the spin tub passed through its critical speed. If an unbalanced condition is detected as the spin tub passes through critical speed, the spin speed is maintained below 300 rpm.
U.S. Pat. No. 3,425,559 discloses an automatic washer having a single speed motor and a two-speed transmission, along with control means for maintaining the transmission and low speed setting during the initial portion of the spin to reduce the load of the motor. Once the motor speed reaches a certain percentage of its maximum speed, the transmission is shifted into its high speed mode, thereby increasing the spin speed to its maximum. This is done to prevent stalling of the motor at the start of a spin cycle of operation.
U.S. Pat. No. 3,526,105 discloses the desirability of keeping the spin speed low to maintain good performance when laundering permanent press fabrics. The disclosed control operates a pump at high speed during an extraction portion of the wash cycle and operates the motor, which effects rotation of the fabric basket, at a high speed until a portion of the liquid has been removed, which is sensed by a level sensing switch, at which time the motor will be energized at a slower speed through the remainder of the extraction portion of the cycle. It is stated that the full tube of water prevents high rotation speed of the inner basket when the motor is energized at a high speed.
U.S. Pat. No. 4,513,464 discloses the idea of providing controlled acceleration to the drum of a centrifugal extractor to minimize unbalance problems. In particular, the speed of the drum is held constant until the amount of load unbalance drops below a certain level, after which the speed is increased and the unbalance is again measured. This patent also discloses the idea of measuring the difference between successive unbalance measurements, for the purpose of controlling the speed of the drum.